Servo-control device for raising tractor-hauled equipment



D. FAURE July 13, 1965 SERVO-CONTROL DEVICE FOR RAISING TRACTOR-HAULED EQUIPMENT 7 sheets-smet 1 Filed May 16, 1965 DANIEL FAURE l N V NTO R Bv-f/fpf @M ATTURNIYJ' July 13, 1965 D. FAURE 3,194,319

SERVO-CONTROL DEVICE FOR RAISING TRACTOR-HAULED EQUIPMENT Filed May ie, 1963 '7 sheets-sheet 2 DANIEL FAURE INVENTOR ATTORNEY-f D. FAURE July 13, 1965 SERVO-CONTROL DEVICE FOR RAISING TRACTOR-HAULED EQUIPMENT Filed May 16, 1953 7 Sheets-Sheet 5 gli Q S um N: om vv M; Q wm n mm mm ,Y E Nm. mi MH. Q. `mw mm mv l- Il DAN/EL FAURE NVENTOR. v-M'ulk TTORNIYJ sERvo-coNTRoL DEVICE EoR RAIsING TRACTOR-HAULED EQUIPMENT Filed May 1e, 1963 D. FAURE July 13, -1965 7 Sheetsa-Sheei'l 4 DAN/EL FAURE July 13, 1965 n. FAURE SERVO-CONTROL DEVICE FOR RAISING- TRACTOR-HAULED EQUIPMENT 7 Sheets-Sheet 5 Filed May 16, 1963 DANIEL FAURE INVENTOR.

ATTORNEYJ July 13, 1965 D. FAURE 3,194,319

SERVO-CONTROL DEVICE FOR RAISING TRACTOR-HAULED EQUIPMENT F'iled May 16, 1965 7 Sheets-Sheet 6 /f DAN/EL FAURE lNvENron ATTORNEYJ D. FAURE 3,194,319

SERVO-CONTROL DEVIGEFOR RAISING TRAGTOR-HAULED EQUIPMENT July 13, 1965 7 Sheets-Sheet 7,

Filed May 16, 1965 ATTOKNEYJ United States Patent() 21 claims. (Ci. 172-9) This invention relates essentially to a device for controlling a servo-action mechanism as a function of two magnitudes such as the position of an element and the force exerted by this element, this device being applicable notably to equipments coupled to farming tractors or the like.

The device according to this invention is remarkable notably in that it constitutes a servo-action mechanism for example of the hydraulic servo-motor type energized from a pump for controlling the raising and lowering of a soil ploughing or like instrument coupled to a tractor automobile vehicle, for example of the farming type, by means of a so-called three-point coupling, of the type comprising a distributor of compressed fluid which is interposed preferably in the delivery circuit of said pump and comprises a control memberkin the form of a multiple-port three-position valve providing the feed or raising position, the stop or neutral position and the exhaust or lowering position, said valve monitoring said servo-motor consisting of avhydraulic single-acting cylinder adapted to be controlled separately at will through the mediumy of a selector device controlled in turn by means of a two-position hand-lever either by the position of said instrument or by the tractive effort exerted by said vehicle which is measured by a transmission device of said third-point coupling, said two magnitudes being stabilized respectively to an adjustable value set by the very position of a same control hand-lever and controllable at will by said last-named lever, this device being remarkable notably in that it comprises two transmission mechanisms of the linkage and positive drive type constituting two separate kinematic chains for the aforesaid two servo controls respectively, each chain connecting the aforesaid hand control lever to said valve, one of said transmission mechanisms being also connected to the shaft or lever controlling the raising arms, the other mechanism being also connected to the effort transmission device at said third point of said three-point coupling. These two parallel servo mechanisms of same design arevthus positively connected through pivot pins housed in straps or tenons without resorting to any cam, roller or feeler or like costly friction elements likely, by their inherent inertia and play, to interfere with the precision and quickness of response of the control. Thus, the movements of the driven members take place positively in either direction.

The device according to this invention is characterized by an increased safety of operation due to the combination of the spring recovery effect introduced into the device in the raising direction, to the provision of a stroke-limiting rod acting directly on the valve, and to the evolutive connection between the two kinematic chains land said slide Valve.

Other features and advantages of this invention will appeark as the following description proceeds with refer ence to -the accompanying drawings showing typical forms of embodiment of this invention given by way of example only, it being understood that the invention should not be construed as being limited to these specific examples since many modifications and variations may be brought thereto without departing from the scope of y maiala Patented July 13, 1965 ice the invention as set forth in the appended claims. the drawings:

FIGURE 1 illustrates diagrammatically in side elevational view a farming tractor hauling a plough equipped with the control device of this invention;

FIGURE 2 is a perspective view showing on a larger scale, as seen from the rear, the three-point coupling and raising mechanism;

FIGURE 3 illustrates diagrammatically on a larger scale a side elevational View of the third-point connection mechanism; 'v

FIGURE 4 illustrates diagrammatically a part-sectional view of the hydraulic circuit of the device according to this invention;

FIGURE 5 illustrates diagrammatically in section and on a smaller scale a hydraulic distributor having its component elements disposed in the raising position of the valve;

FIGURE 6 illustrates diagrammatically a section taken upon the line VI-VI of FIGURE 5;

FIGURE 7 illustrates diagrammatically a section taken upon the line VII- VII of FIGURE 5;

FIGURE 8 illustrates diagrammatically a sectional View of the distributor with its valve in neutral position;

FIGURE 9 illustrates diagrammatically a section taken upon the line IX-IX of FIGURE 8;

FIGURE l0 illustrates diagrammatically a section taken upon the line X-X of FIGURE 8;

FIGURE ll illustrates diagrammatically a sectional view of the distributor with its Valve in the lowering position;

FIGURE 12 illustrates diagrammatically a section taken upon the line'XII-XII of FIGURE l1;

FIGURE 13 illustrates diagrammatically a section taken upon the line XIII-XIII of FIGURE ll;

FIGURE 14 illustrates diagrammatically in perspective view the complete servo-control device according to this invention;

FIGURE l5 illustrates separately and diagrammatically in perspective the position control servo-action kinematic chain;

FIGURE 16 illustrates separately and diagrammatically in perspective the effort control servo-action kinematic chain, and

FIGURE 17 illustrates diagrammatically in perspective a modified embodiment of the device shown in FIG- URE 14.

In the specific and exemplary form of embodiment of the device which is shown in FIGURE l, the reference numeral 1 designates a farming tractor to which an equipment or implement 2, for instance a plough, is attached by means of a conventional coupling or trailing hitch 3 of the so-called three-point type. This coupling comprises two side arms or draft lin-ks 4 having their rear ends pivoted on a horizontal shaft 5 or a pair of horizontal pivot pins 5a carried by the plough head and their front ends pivoted likewise on a horizontal shaft 6 carried by the tractor chassis, preferably substantially beneath the driving rear axle of the tractor.

A third point connection 7 comprises -a rigid arm 8 consisting preferably of two sections assembled by a tensioning device 9 into a top link and pivoted at its rear end on a horizontal pin l@ disposed at a level substantially higher than the front end of the rigid arm 8 and carried by the upper end of the plough post, this front end of `arm 8 being attached by means of a thirdpoint coupling device 11, in a manner to be explained presently. Preferably, all these pivot pins or shafts are mounted in ball-andsocket or swivel bearings to afford a certaindegree ofy free lateral motion for the instru-V ment or-equipment, the movements in the vertical plane being controlled by the raising device proper.

Mounted on the rear portion of the tractor is a raising control unit 12 bolted or otherwise secured on the frame Vof the tractor and ,comprisinga V:huilt-in oil sumptor -f reservoir. This yunit communicates with -ahydraulic pump 13 secured on the power unit `and driven from the tractor motor either through a belt from za power take-oit or the timing pinions-of the-motoig-,or through any other means atv any suitable pointfon thetractor. This pump draws oil from the lunit, `12`through a suction pipe line 14 Iand delivers it through a'pipe line or transmission line yof the adjustablelength type Which connect the arms 1S to the relevant coupling rds74, the suspension arms '19 being pivotally connected to these rods at an intermediate point .19a thereof (see FIGURE 2). The servo-action mechanism is controlled'by ahanddever 2@ andthe selec- Y tion from-ftheeiTort-responsive control to the positionresponsive controlor vice-versa is eifected by means of a selector or change-overlever. `21. Y

The third-point coupling device 11 (see FIGURES 3)V comprises a movable support in `theform cfa strap or yoke' (rocker member) 22 pivotally mounted on a substantially horizontal pin or lug `23 consisting preferably f of a horizontal spindle icarried for example by a lug ,or

boss projecting from a gear-change transmission case 24.

of the tractor. Severalsuperposed pairs of aligned holes (for eXample'three-pairs,-25, 26 and 27) are formed through this strap 22 for adjustably coupling the arm '8.

to thestrap bymeans of a detachable spindle 8a.,V The front face lof strap 22 contactsia'pair'Y of elastic pads 28,

29 disposed on either side respectively (that is, above and f beneath) of the horizontal;pinl23 and pre-stressed in the Iassembled condition. Y

v When the instrument or tool 2 is pulled by theftracton V1 theside arms'4 are subjected `t0 a tractive efIortWhile ing Works in a controlledposition: 1

mission, 'orthe'likeY The beator oscillation of strapj22 isLlimitedin either direction by a pair' of adjustable stops.132,;33 limitingthej Y vcompression fof the elastic jpads.28,fj29 iin order Ato :deter mineV the maximum value vof the vstraposcillationand n therefore Aof the Vtractive` and.V Ycompressiveelforts applied Yto the third-pointarod,8.5V The relative swingingzo lever 30 isralso limited byfapair of"adjustable' stops-34, '33953505V` disposed thatfthemaximumxangular amplitude ofjlever 30;.betWeen-stops `3,4and 35V correspondssubstantiallytol J the maximum permissible angular -beat jof'fstrap V2,2.-

the upper arm.8 is compression stressed to resist the tendency .of the instrument `2ftotilt upwardabout 'the axis- 5. When the `tool is -relativelyheavy and Vthe load applied thereto during its operation is relatively moderate,

the upperarm mayalsobe subjected toa tractive effort due to .the vpredominance yofthe weightof the toolof which the overhangeffect'is not suliicient to balance the f preceding tilting. moi-nent. -When vthe r:upperi arm 8 is compression-stressed, it `.compresses in turn theelastic.

pad V2S and at the same time the ei'l'ort appliedrtoV the lotherpad 29. is reduced and mayY even be cancelledor reversed. Thus, to any compressive iorntractiveeiort. .applied tozthe varm 8 there ,corresponds a single position of the third-point strap 22. If the upper .armSds at-y tached by inserting the spindle 8a through the'lowermostVv i pair of holes =27 which isnearest to the horizontal pivotA 23,.a very considerable reaction will be necessary to v `compress the pad 28. e

On the. other handgan effort of same magnitude will 5 compress this pad to a greater extent if'the spindle Sar-is .i

inserted through thentermediate pair of Ialigned holes 26,

This third-point coupling system-iis. already known? per. se and has been-described` herein for, explanatory Vpur-` Y poses only land shouldynot be construedyas"lirniting'the d present ;invention',fas`other equivalent means may .be-used with corresponding ieiects.

Y Aswill beexplained=presently,5fto any positionof the i loweringa'nd raising control leverglftherefcorrespondsa Y single position of the; input leverfai) atV which the valve t Y. Ymember of the internald-istributorjfof unity 12 assumesfa Y Y neutral :position while stopping-the* operation` nf` the raisf ing mechanism.` Fromrtheselrelative positions pfequilib.- L Y. n rum any displacement; in ,any` idirectionfwilll produce a i servo-action tending ,to restoregthe finitialwequilibrium-f 2 .Thus, when thewsoil--portion :engagediby'tool=orinstru -k ment 2 is lessfrunnin'g-,thamthe preceding lonelthencompression stresses applied-to -the upper armi ffin'-creases,` and thethir'd-point Astrap v22 is tilted forwardsitomove 'thereV7 input lever 30;* Thus .the Ainternalservo-actionjbecomesoperative Vto raise the Iarms 18 andthereforethel toolY Z in order toreduceits depth of penetration an'djtherefore f itsY resistance toV forwardmotion. .Y @Thislmoyement will cease when the: compression `effort-exetred:,onlvarmV 8 has resumed its-initial value.V Vi' y in `a'soil having variablef'characteristicsrandwhen reof the effort exerted by the arm `8 is moved away from the axis of rotation of strap 2.2, ;the lever. arm increases.

Under theseV conditions, it is :clear that vthe higher the:

position of assemblyspindle 8a, the greater` the sensitivity ofthe coupling toftractive citons. ,Thus, under normaliA operating, condtions it will befadvisable -to use the upper holes 25 for surface and light Works, the lower holes27: for heavy works, that is, when a majorV sensitivity is not required or When the soil-is of heterogeneous character,

actions aref-produced inthe coupling ,system as,l a conse quence` ofthe tractor .movementsfdue Vto vthe clearing of ground unevennesses,F vwhether V,of 1 natural on artificial character,bytheftractorrwheels ortracks f Y' FIGUREA illustrates a-typicalfdiagram@of the, hy. "draulic, circuit, showing in section the Vtool Vraisingpunit)l2 comprising in :a common lcase for housing constituting an f Vintegral oil sump or reservoir a'hydraulic' distributor or@V control mechanism .36 and .-aV singleacting Ahydraulic cylinf der orram unit icontrolling throug'hadswive'l, orlballf and-socketetype zlink .(piston rod), 38V a fork' orf'socker lever, Jor drivej arnr 39 rigid; Withthe raising shaft 117.

servo-actionmechanisms.,. f i Y Y 'j 5 The hydraulic distributorj deriving ior example from `a known vtype used notably in rloadV-tr'ansfer"'hydraulic systeme, comprises'a single three-Wayrotary valve! mem-,

ber or plugk 400i which acontrol shaft?lllcarriesex-Y te'rnally'a crank web 42 adapted `tofbe1connected directly n i through a crankpin 43 to either othe two servo-action mechanisms or'kinematic chains.Y The :valve rrnernberft provides a constant communication between a pressure- 74%. the'central holes 26 beingprused for example forperfornlV 'Y i and on the other hand a feed and relief spring-loaded check valve 47 inserted in a feed and return circuit or duct 48 connecting the distributor to the cylinder.

This last-named valve 47 (acting also as a non-return valve) is normally urged by -a spring 49 and the oil pressure in the cylinder to lits closed posi-tion, but it can be opened mechanically by the rotary valve member 40 in a predetermined position thereof, by means of a cam or like member 50 solid with the rotary valve member and registering with said valve 47 engageable by said cam or the like. The piston 46 acting as an exhaust valve is slidably mounted in a chamber 51 of the distributor body .and responsive to the permanent action of a return spring 52 urging said piston to its closed position in which it engages a frustoconical or like seat 53 to close the exhaust port 45. The rear face of piston 46, together with chamber 51, may be put in fluid connection with the inlet port 44 by means of the rotary valve member 4t) at a certain position thereof, by means of a duct 54 formed in the distributor body and leading into the chamber 51 and also of a passage groove or duct 55 formed in said rotary valve member and adapted to register with the duct 54.

In another valve member position the chamber 51 may also be connected to the oil sump through another passage groove or duct 56 to permit the escape of the oil contained in this chamber 51. Finally, the rotary valve member 40 is also formed with an exhaust duct 57 constantly communicating with the inlet port 44 and normally closed by a safety or overload relief valve 58 leading controlling the access to the oil sump. The passage 57 has on the other hand the function of balancing the rotary valve member in the radial direction since this passage 57 opens through the peripheral valve surface, preferably at a point diametrically opposed to groove 5S, thus easing the operation of the Valve member and reducing friction wear.

As already stated, the rotary valve member 40 of the distributor may be set in three positions, namely a neutrai or inoperative position in which the cylinder piston is kept in its momentary position by the fluid under pressure, and two positions, that is, a raising or cylinder-feed position and a lowering or cylinder-exhaust position, Ithese positions being located on either side of the neutral position. A very small angular movement of the rotary valve member on either side of its neutral position will cause fluid under pressure to be delivered to, or exhausted from, the hydraulic cylinder. In the tool-raising control position illustrated in FIGURES 5 to 7 of the drawings cam 50 is moved away from valve 47 and the passage groove S5 registers with duct 54, whereby oil under pressure flows into chamber 51 and, due to the combined action of the oil under pressure and of return spring 52, piston 56 is urged against its conical seat 53; since in this case the cross-sectional area of the free front face of piston 46 in exhaust duct 45 is smaller than that of the rear face of this piston, when the oil pressure increases in the distributor ducts this piston 46 Will remain in its closed position due to the direction of the resultant of the hydraulic forces thus set up. Due to this increasing oil pressure, the valve 47 is moved back and oil under pressure flows into cylinder 37.

In the neutral or stop position illustrated in FIGURES 8 to l0 of the drawings the communication between chamber 51 and the inlet port 44 is discontinued and this chamber is connected to the exhaust through the groove 45 now registering with duct 54. The oil trapped in chamber 51 will thus escape to the sump and piston 46, due to the hydraulic pressure applied to .its front face, will recede, thus uncovering an outlet port 45 of exhaust duct 45 to the sump. Valve 47 is reclosed by its return spring 49 and by the oil pressure in the cylinder. At this time, the cam 50 of Irotary valve member 40 just contacts-without any appreciable pressure-the valve 47 which maybe of the mushroom or poppet type.

' In the lowering control position illustrated in FIGURES 11 to 13,. the chamber 51 is constantly connected to the exhaust through groove 56 and due to the complementary rotation of the rotary valve the cam 50 lifts Valve 47, thus causing the duct 48 of the cylinder to communicate with the exhaust duct 45 in which the exhaust control piston 46 is easily pushed upwards, so that a corresponding pressure drop takes place.

FIGURE 14 illustrates the complete double servoaction mechanism connecting the rotary valve 40 of the distributor respectively to the raising lever 39 on the iirst hand and to the third-point coupling device on the other hand, and to the hand control lever 20, together with the selector system.

FIGURE 15 shows the kinematic chain or mechanism responsive to the controlled position. The hand control lever 20 is mounted on a rotary plain shaft 59 mounted preferably horizontally in a bearing of the raising unit 12, this shaft 59 comprising a crank web 59a having journalled on a crankpin 60 the lower end of a rocking lever or link member 61 adapted to oscillate preferably in a vertical plane, for example a plane parallel to the longitudinal vertical plane of the vehicle. The upper end of rocking lever 61 is pivoted by means of a pin 62 on a follow-up link 63 connecting the lever 61 to the raising lever 39 on which the link 63 has its opposite end pivoted by means of a pin 64 rigid with lever 39, as shown. Elements 63, 61 and 66 together form what may be termed a first linkage.

The rocking lever 61 is pivotally connected intermediate its ends, at 65, to one end of a variable compound connecting-rod or force-transmitting link 66, preferably of the elastically deformable type, the opposite end 67 of this rod 66 being connected to the crankpin 43 of crankweb 42 solid with the rotary valve 4i). This crankpin 43 consists for instance of a stub shaft extending at right angles through the crank-web 42 so that it projects on either side of this web 42. The deformable connecting-rod 66 is deformable in only one and single direction from its. initial` or rectilinear state, and consists preferably of two movable arms, portions or sections 68, 69 pivoted on each other at a point 70 and constantly urged by elastic means such as a spring or like element 71 having its ends attached to these arms 68, 69 to their mutually aligned position, that is, the position in which they are substantially co-extensive. This aligned position is determined by a stop or abutment'72 solid with one of the arms, for instance arm 69, and adapted to engage in the aligned position the lower edge of the other arm 68. Thus, due to the provision of this stop 72 the compound connecting rod 66 can be folded in one direction only and in this example this direction is the downward direction as far as pivot pin 70 is concerned. The two arms may advantageously have different lengths, the arm 69 connected to the rotary valve 40 being preferably shorter than the other arm 68 so as to constitute somewhat a kind of pivoted extension thereof. One of the two arms, preferably arm 68 connected to rocker 61, is adapted to cooperate with a corresponding member of the aforesaid selector system. The other arm 69 is connected to the crankpin 43 of the rotary valve crankweb by means of an elongated hole or like aperture formed in the end portion 67 of connecting-rod 69 and engaged by said crankpin, the contour of this slot being designed with a View to permit, according to its relative position, the engagement or the disengagement of the operative connection with said crankpin under the combined effect of the controlled action exerted by the selector system and of the attendant deformation of the compound connecting-rod 66.

Preferably, the aforesaid elongated hole or like aperture is substantially T-shaped, its upper transverse portion constituting a substantially rectilinear elongated aperture, slot or slideway 73 substantially parallel to the longitudinal axis of arm 69. This slideway is adapted,

movements of combined translation and `rotation of.

the crankpin 43x! Y crankweb 42 and arm 69; The otherpo'rtion of the" i T-shaped aperture,fwl1ich extends substantially at right angles to theslideway 73",fconsists of Van elongated blind j groove74 .preferably substantially rectilinear and con,- stitutinga kind ofthollowed orv engagedY transverse notch" permitting Vonly the relative angular movement of crankweb. 42 and arm`69 When theV crankpin 43 engages the bottom of groove 74. t

A ,preferably resilientmember, such as at least one Y drawback spring '75 Vor the like,; is provided for con.

stantly urging the connectin'gfr'od' 66l(by acting .preferably on its arm68v)on-the one hand in the directiony toy engage the crankpiny43 into Vthe aforesaid blind groove.

74 and Ion the other hand toward the'position in;which itis operativelygconnected with the aforesaid, selector system. The spring 75 which,vin,the present instance, is a tension spring, is attached for example byfone end toa xed point (lug) 76 and by its'other end to a point t 77 ofarm 68, preferablyin the vicinity ofthe pivot pin 70. The crankweb 4Z is advantageously provided, be-V -yondrthe shaft 41 of rotary valve 40, with an `extension- 78 responsive to a play take-up spring 79 havingrits other end attachedto a xed point or bracketl 30.V Thisspring t 79, 'preferably V of the tension type, `is thus causedto con-` stantly urge the crankwebt42 in the direction to rotatethe rotary valve counterclockwise, Vas seen in thev FIGURE, that is,in the direction to lift the raising arms 18;;

An adjustable'de'formable rod (pull rod) 81 connects Vthe raising lever 39' to Vthe crankpin'43 of vrotary-valy'e 40. l YTo vthis endfthis rod has one end pivoted on said crankpin and the other end pivoted preferably on the pivot pin 64 on which the aforesaidtlink 63 1s also prvf oted. This deformable rod 81 is deformable only in one direction from an initial conditionof maximum adjusta-r`r V ble elongation, andi consists'advantageously of two mova-` `ble sections or arms 82, 83, if` desired also of unequal lengths, which are pivoted oneach other at. an intermediate ,point 84. An adjustable stop SSfVor example* Y ofthe screwat'ype is provided on one of'these arms,'-for Y example arm 32,for determining the Yinitial position of maximum, relative spacing Lof Ythetwo arms which sets the Vdistance between centers of, or the maximum per-4 missible relative Vspacing between the crankpins 64 of the raising Ylever and 43 of the rotary valve. To this end, a stoptVSS is adapted to engage a portion S6 of arm 83, vthus permitting the possible bending of: rod 81 only Y in thedownward direction of movement of pivot pin 84 which,V to this, end, lies below the plane `containing the, axes of thetwocrankpins 64 and 43.

FIGURE 16 illustrates the kinematic chain or mecha- VV'nismservo-responsive to the controlled effort, wherein the displacement occursl likewise preferably in a sub-Vv stantially vertical plane parallel to that of the preceding chain.

lever 20 to the crank-Web ,42 of rotary valve 40 are advantageously completely similar if notV identical, from the,

organic and functional Vpoint of View, with the corresponding or homologous elements of the servo-action chain of FIGUREVllS. The chain illustrated in FIGURE Y 16 comprisessimilarly a rockingleve'r or linkmember S7 having its lower end-pivoted onthe same crank-pin 60 third-pointjcoupling 90.V The rocker 87 is pivoted Vinter- Y mediate its ends,v at point 91, on one end of a deformable connectingrod or force-transmitting link 92 ,havingA its other end 93 connected to the crank-pinV 4310i the rotary The ,component elements: of this chain which Y connect the crank-web 59a rigid-with the hand Ycontrol valve crank-web This lcrankfji'n 43`vis'thus,'alsoiknowrrf i tothe two servo-action chains,tsin'ce it isconnectedt'o ther two deformable connectingfrod's- 66 and L92,1: (of these two and SZmay,l in turn, lbe termed a second linkage. Y

The Vdeformable connecting-rod 92 isY also'co'mprisecl;Y likev rod V66,0f itwoj'armszor portions94',95upivoted on :y each other at a pin-96 and adaptedato befolded'inY 'only' oneVV direction,thatV is, the direction offthe:downwardY movement of pivot pin96, dueto the' provision -of a'stp v or abutment 97 'carriedfor instance Vby, thef'armf95 andi adapted Vto engage the ylower edge of arm-94v when ,thesei twoar'ms have resumed their initial, substantially. alignedv V'relative position in which theyf areV cov-extensive. VA` ten` sion or like spring 93 having itsends,` attachedftotthetwo arms- 94, 95. constantly ,urges these ,armsV Tito their afore-fV f said'alignedposition. t "1 the aforesaid selector system, gisjresponsive-tothe vperinanent` load of a ytraction or-likespringal' attachedby one end to a fixed point (lug)V- 1022by1its' oppositeend to aki point 103 Aof V"connec-tinglrod 92, preferably V'on 4the yarm 94 and in the vicinity of the Vpivot pin" 96 thereof;

w The pivot pin YS8 connectingtthej link' 39ffandv rocker f 87 ,consists advantageously of a deviceacting like an afl- ,V justable eccentric adapted toideter'mi'nethc amplitude'of'1V angularV movement between V.link l the permissible relative 89`and rocker871y The transmission device90'of the"'third-pointV coupling comprises a crankshaft vorliketrotary member 104gincor- Y porating `two crank-webs or: arms 30,"and105isogtas to"V Y formv a bell-crank 'lever'. d Crank-Web 30' t constitutes-'or is solid. with. ,the t aforesaid input lever Slthi'andthe; ,other -Y crank-web 105 Vis pivoted by'its endgltl'onthe Vend of ,Y Vthe aforesaidk link 89.1' The crank-web 30f-isidis`placeable v between the aforesaid .limit stops134 and 35,?,one stop 34" corresponding ,toV ,the `rninirnumfeffort and the 4other?` 35* to the maximum effort! It-Lxxnay be `noted:that'in:FIG-1v URES-14 andrl, [the relative Vpositionsofcrank-Web V311Vk v -and stopmembers 34 35 are reversedf'iespectively in relation to those fof the inputtlever 30A andtstops 34 and 351 I illustrated in FIGURES 1'to ',3 of thedrawings; Y

In fact, the form,of'embodimentshownin FIGURES 14' and 16 may correspond to atleasttwo different variai tionsboth applicable differently(V In a iirst*variation,`fthel Y input leverV 36 wouldV have'the position illustrated y in FIG- URES' l` toer?,Y (that is, directed upwardly) 'paridwould -be t the latterwvouldact simply as a movablecounter-stop adapted to engage, the adjustableV stationary stops 34 andV 35. In the othery variation Vthe'input ,leveniSG fconsistslof the crankfweb tVpivotedbylits ,lowerendonithe adjustable V connecting link 31, yand, thepivotpin V26 of upper arm 9 =is assumed Vto lie beneath the pivot pin 23 kof strap 22, that is, on the side opposed, with respect toV this pin 235,1? tothat ofthe pivot pin-l'a'of link 31 (seeFIGURE 'The selector,- or `'chan'ge-'over` systemi'designed for-put`V`v ting into operation Vone of theV servo-action chains lori e mechanisms while simultaneously trende'ring theM other .servo-'action chain or,` mechanism`inoperative, and vice` versa, is illustrated in ,FIGURE vr1'4 showing the complete assembly of the two. servo-action'mechanismsV orgcha'ins. This selector system comprises a pair of V,cams or like dis-1V connectingjmembers 107,108 mounted' on a Icommon,I `cam shaft or tumblingshaft. ltcontrolledibythe afore-v said selector lever disposed preferably in a horizontal position and carried by stationary bearings or supports 111i.

In case the two rocking levers 61 and 87 were identical, as well as the two deformable compound connecting-rods 66 and 92, the two cams 1117 and 1% will advantageously also have the same shapes and dimensions, and will overlie said two connecting-rods 66, 92 so as to engage either of them, for example their respective arms 63 and 941, in order to lower the arm contemplated and thus fold each one of these deformable connecting-rods about their intermediate pivot pin 70 and 96. To this end, the aforesaid cams are designed to have an evolutive contour and such a relative mutual direction that when one of said cams causes its companion connecting-rod to be detlected downwards, the other cam permits the eX- pansion or straightening of the relevant connecting-rod, whereby the latter can resume a rectilinear configuration under the iniiuence of its return spring 71 to 98.

When one or" these deformable connecting-rods is thus folded downwards by its companion cam i-ts short arm 69 or 95 is caused, in this broken configuration of the connecting-rod, to assume a disengaged or released connection position with respect to the crank-pin t3 of rotary valve crank-web 42, wherein this crank-pin engages the slideway 99, and on the other hand when the connecting-rod resumes its aligned configuration it is ready to be engaged by the crank-pin 43 which, in a suitable position, is likely to be moved to the bottom of the substantially vertical groove 74 or 101) under the influence of the return spring 75 or 101.

The contour of cams 107 and 1113 is so designed that when the selector control lever passes at a predetermined intermediate position, both deformable connecting-rods 65 and 92 are bent simultaneously to a transient folded position in which their connection with crank-pin 43 is acted upon, whereby this crank-pin 43 is engaged in both slideways 73 and 99 simultaneously.

The cam shaft 1119 may be rotatably driven from a crank lever 111 solid w-ith one end of this shaft and havling its other end pivotally connected to the selector lever 21. To this end, the selector lever 21 is solid with a preferably tubular (hollow) rotary shaft 112 mounted coaxially on shaft 59 of hand control lever 2t). The tubular shaft 112 incorporates a crank-web 113 connected to crank lever 111 through a link 114 pivoted at 115 on the crank-web 113 and at 116 on crank-web 111, as shown. The operative connection between shafts 169 and 112 may of course be effected through any other suitable means, for example through gears.

The selector control lever 21 is displaceable in a guide groove or slot 117 formed in a circular sector 11S providing a fixed positioning thereof. This guide groove 117 comprises at either end two notches or gabs 119, 120 corresponding to the possible positions of the selector control lever 21, the latter being engageable in these notches and retained therein by its inherent resiliency.

The tool raising control lever 20 is displaceable against a vertical or like area 121 provided preferably on the same positioning Isector 118.

This lever 20 comprises a clamping device 122 for automatically holding this lever against motion in each one of its positions by simple frctional engagement. To this end, this device 122 is advantageously of the resilient clamping type consisting for example of a screw or like member 123 adapted to move bodily with the lever 241 (on which it is secured) in an arcuated groove or slot 124 formed in a side flange of sector 118. Threaded on this screw 123 are a washer 125 and a coil compression spring 126 retained by a nut 127 screwed on the screw end. The purpose of the spring and washer assembly is to resiliently press the lever 2t) against the edge or flange of sector 118 in order to produce a frictional force sufcient to hold the lever 2t) against motion, in spite of any parasitic forces likely to be exerted thereon.

The permissible angular stroke of control lever along sector 113 may be limited in either direction by at least two limit stops 12S, 129 of which at least one, preferably stop 128, is adjustable along the sector 118. The other stop 129, which if desired may also be of the adjustable type, may be used for determining the lowermost position of instrument 2, and an additional movable reference mark 131i may be provided for indicating a, predetermined intermediate position.

The control lever sector 113 is preferably so disposed that the level of its left-hand or rear end (as seen in FTG- URE 14) is higher than that of its right-hand or front end, whereby the uppermost left-hand portion of the sector will correspond to the maximum raised position of the raising arms 18 and the lowermost right-hand portion will correspond to the maximum lowered position.

The selector system operates as follows: when the operator wishes to switch for example to a controlled-position servo-action operation, he moves the selector control lever 21 to the position shown in FIGURE 14, so that the lever engages the notch 119 in groove 117 of sector 113. Assuming that this lever movement occurred from its extreme left-hand position as defined by notch 12d, both cams 107, 108, at the time the lever 21 has accomplished approximately half the path from notch 121i to notch 119, will have depressed the arm 94 of deformable connecting-rod 92 so as to bend the latter while simultaneously moving away from the arm 68 of connecting-rod 6d, whereby the spring 71 associated with this connecting-rod 6o will straighten the latter.

The rotary valve crank-pin 43 is thus disengaged from the two slots 74 and 1th? of arms 69 and 95 of the aforesaid deformable connecting-rods 66 and 92 respectively, and engages the slideways 73 and 99 thereof, thereby enabling the rotary valve member to to rotate in the counterclockwise direction under the iniiuence of the play take-up spring 79, since the crank-pin 43 is displaceable relatively freely in said slideways. This rotation moves the rotary valve member 4t) to the position controlling the lifting of the raising arms 18. Gf course, this rotary movement of valve member 4t) under the iniiuence of spring 79 is permitted only if the so-called limit rod 31 is initially folded downwards.

When this movement is completed the operator has completed on the other hand the movement of the selector control lever 21 which now engages the end notch 119. Thus, cam 19S completes the lowering of arm 94 of deformable connecting-rod 92, whereby the upper edge of slideway 99 engages the upper face of crank-pin .13 and the latter can thus move freely in slideway 99 while causing the arm 95 to pivot slightly, if need be. On the other hand, the cam 1117 has moved considerably away from the upper face of arm 68 of connecting-rod 66 to permit a subsequent free movement. The upward movement of the raising arms is stopped (unless it was already stopped initially) at the end of the stroke due to the action of rod S1 which, by acting at the end of the straightening movement upon the crank pin 113 of web 42, restores the rotary valve 419 to its neutral position.

When the operator subsequently restores the hand lever 29 against the stop 123 corresponding to the maximum upward stroke, the servo-action kinematic chain or mechanism will place the axis of symmetry of the nearly vertical groove 74 substantially above the crank-pin d3 and spring will then lift the deformable connectingrod 66 until this pin 43 is engaged home in said groove 74. In this position the servo-action chain responsive to the controlled position is rendered operative or engaged while the other servo-action chain responsive to the controlled effort is rendered inoperative or disengaged.

As a result of this general arrangement the positionresponsive servo-action chain can easily be engaged when the raising arms complete their raising stroke. lf desired, this engagement can be obtained by raising manually the previously unloaded raising arms 13. In case of mis- .ber 40 toward the lowering position.

longer stroke of the servo-action mechanism connected., `Vto leverV 39 will be requiredto restore the valve member agressie ilT handling or misoperation on an area for packing `bare blocks, theservo-action mechanism can still-be easiiy re-YV engagedirrespective ofthe present movements or posi-Vy tions oi the -arms 18, hand lever 2t), input lever 3@ and selector control lever 21j. by actuating only these controls disas` until a characteristic slap is heard, and thus any sembling of parts is definitely precluded.

When the selector control lever 21 is inthe position 'shown in FIGURE 14 the position-responsive servoaction operates as follows: Y

The spring 75 ,liftsA connecting-rodV 66 to'its straight position spaced Vfrom cam 167 so that the crank-pin 430i rotary valve 4t) remains in the bottom of theV substan tially vertical groove 74. The different components of the kinematic chain governing theV position controlare then engaged or in operative shape, and those of theV effort control are disengaged or in inoperative shape, and cranki pin 43, can move freely in the slot 9Ek of connectingfrod 92 held in its downwardly bent position by cam 1%.Vv The v Y pivot pin 70 between the arms 68 and 69 of rod edcannot functionin the direction of the upward'movement due tothe` presence of the stop-forming stud 72 urged by spring 71 yagainst the lower edge of arm 6&3. Thus,the connecting rod 66 may under these conditions be assimilated to a rigid rod as far as the movements to the left or right-hand side of the gure are concerned.v On the other hand, thisV rod 66 can Vbendduring a downward movement.,

lf the operator wishesto control a downwardy m0ve.

, ment of arms T18, he moves the hand control levert) toY the yright or to the front end of sector 118tloat` is,`to

the lower portion thereof (FIGURE 14). This lever 20 is then retained or locked lautomaticallyy by theA device 122. During this left-to-right movement of control lever Zd the cranlifweb 59ay or this lever `rotates in the clock? wise direction (FIGURE ,14) and carries along the lower end of rocker 61v so that the latter rotates about the pin 62 Vand moves in turn the rodeo to the left, together with the valve member crank-pin 43 engaged in thevertical groove 74; `Thus, the rotary valve 4d is moved to the.

pin S4 onlyin one direction 'fromfthe `maxiV iurn'divari- "cated position, that is, downwardly, for VVitsmovement inAV theopposite .direction is limited V,by 4the adjustable screw stop thereby limitingthe VangleiformedV by Varmsi S2 and 83 and therefore the relative. spacing lof crank-pins 64and43.. u Y g Y. Thus, Vthefstop v position at thezendfof theraisingfstroke can be adjusted 'oyssimply movingthecontrol lever YZtl'` to theendmost'left-liand position or Vtothe rearY of, sector Y 1,18 which corresponds Vin practice to its top,"and=to act upon the stop screw SSIwith avieW to causey the distributor.

valve member 40 to attain the'neutral position before v the raising lever 39 abuts against the case of the raisingy Vunit 12, for example. `The hand control leverili; may Vif desired be slightly movable-"to theV r'iglttthat.is''down--V wards or forwards, as a consequence ofthe pivotingmove-.f-

ment to the right of cranlo'pin 43 duet-othe action of rodl, in case frorexamplefthe maximumrfraising position of lever'rZtB corresponds' to an :end position of: armsl inV l the raising directionwhieh exceedsthe, normally lpermiss sible posit/ion as defined by therisk VYofinterference for Y instance ofA lever'39 with thecase of the;` raising unit12."

A To avoid thisinconveniencmvthe variablefstoplZSwill 'Y be moved; (for examplefby sliding in the groove 1241,05 j sector 118).until'thenewposition determined by thegrev turnmovement of the, rotary valve member'40junde'r the v influence of rod-.S1` isV attainediri order to avoid any subsequent uncontrolled-movement of lever v2i).V` -If this adjustment is 'Y properly made,. no further intervention .of g

rod S1 will be `necessary for controlling. the position. .1

It may benoted` ,that the provisiony offaV deformable rod. VSil does notinterfere whatsoever{withgthe- ,servo-action..

InY fact, if from an initial left-"hand or1upperposition the Y operator moves the` control'v lever V 20 Vtopthe `right-hand Vvor lowering position, the crank-,p'i'ni ofirotaryvalve 0f will move tothe left, thus reducinggthe distance between f. l, centresofncrankrpins V64 and43 of lever 3) and crank-V web 42, respectively. VThis`reduotion-isf` noti` impaired by clamping Vdevice 122, the rocker 61 will pivot in ,the

clockwise direction (FIGURE 14)' about the crank-pin 6i), thus moving ,the connecting-rod 66 and'therefore the` Acrank-web 42 ofV rotary valve `It@ of distributor unit i2 to the right, 1until this rotary valve d@ is in neutral posiaV tion and stops the downward movement of arms 1S.` and therefore the rotation of raising lever V39whereby. this leve-r 39 is heldin a position corresponding to that of control lever 20. It isclear that'under thesel conditions,.

the rod S1' when ithe latter is', bentlgdownwards about its Vpivot pin S4 vbeing lowered,fsince,tlnspin 84jis always!-VVV located beneaththe'imaginary. straight'linegdrawn,-be-Y tween thel axesof cranl'pins gf-iand 43.A lf under these conditions Y'theopelrator sector 113]# v, Upon completiongof its Ystrolrepthis lever will engage .the retaining notcha1`20rf/,The selector or i -engagement/disengagement mechanismhaving voperated the more the control lever Zis moved towardthe lower end of the sector, the greater they rotation Yof valve mem- 40 toits neutral position. f Y

If the operator wishes to control an upward movement Therefore, Ia v of the vraising arms 18, he moves the lever 21H0 theleft, 1

or to the rear of sector 11S (that is7 toward the top of this sector as seen in 'FGUREv 14). vThe servo-action mech-f anism operatesV under the sameV conditions but in the op positerdirection to restore the rotary valve member Mito its neutral position, andtinally the, complete-system tota position corresponding tothe present position of control lever 20. Thus, to each position of control lever 21B there*corresponds ka position of arms 1S. This applies to all the positions of leverZt except the maximum raising position in 'which the movement is stopped b y :asA explained 1 hereinabove, Y connectingrod ,92 j is straight: Y and freejfrom camiltld, andxthe rotary 'valve crank-pin wislesf'to,switchE4 to servoaction responsive to the `controlled eftort, heV l moves-the VYselector vcontrol lever v21' from theiporsitionf illustrated in FIGUREfWlAtY to-th'e left or tofthe rear .oft

substantially vertical ,groove 100., The difterentcompo-V trol ,are .then rengaged'. On thef other hand, .the vposition controlmeansare disengaged for rod 66'is kept *in its,r f bent orV broken'V position kby cam 167v and crank-pin 45;

can move freely along thesli'deway '73`of'rod 66.

The input leverltl or itscranlr-web 3:0r connected to y* Y Vnentelements ofthe mechanism governing the eifort' con-1- the'third-,point strap 2,2 through the adjustable?connecting and stop '55 to theV maximum ystress transmittedlthroug'h linlefl is displaceablebetweentheitwogadjustable .stops-g 34 and 35. Stop. 34.correspondstotherninimum stress -strapl-ZZ.` This minimum Vstressfmayliave rany. desired value, ffor'example zero,'^'or:a positive` value,'.that is, cor-K.y 1

responding to afcompressionfor'e exerted-"on ftheljinkgl, j Vor even a negativevaluejthatis a value corresponding toV a tractive elort Vexerted on this link31`f; VInthis case one' of the -elastic pads ,128; 29.l is'fexpanded instead` offbein'g compressech- Assuming thattheinput :lever [30, {or'iits web 3G', engages therstop-p-34, itgmeans that ythiselement Y is in its minimuin'stress, position. Whenthe operator means of the deformable connecting-rod S1, vln fact,

the arms S2 and of this rod` can pivot about the pvot wishesto control the: upward movement of raising arms Y d, he Ypusheszthe control lever12f0 againstV its-limit stop.

128 corresponding `to the end yof the raising movement. Y

The crank-pin 60 then pivots to the right and carries along the'lower end of rocker 87 so that this rocker will pivot in turn about the eccentric SS while pushing the connecting-rod 92 and therefore the crank-pin 43 of the rotary valve member to the right through the pin 91. The distributor valve 40 is thus brought to the position suitable for controlling the raising movement and the fluid under pressure delivered to cylinder 37 drives the piston back and therefore causes the lever 39 to pivot to the left with its crankpin 64. The distance between centres of crankpins 64 and 43 increases until the spreading movement of the two-section rod 81 is discontinued and crank-pin 43 is moved to the left for finally restoring the rotary valve member 40 of the distributor to its neutral position, thus stopping the raising movement and causing the pump 13 to deliver fluid to the oil sump 12.

During the period preceding the return of the distributor rotary valve to its neutral position the control lever tends to move to the right somewhat away from the stop 128 corresponding to the end of the raising movement. In fact, the two-armed connecting-rod 92 is carried along to the left by the movement of crank-pin 43 to its neutral position, whereby crank-pin 60 is rotated to the left (FIGURE 14) and the lever 20 solid therewith pivots to the right, since point 88 is momentarily stationary, as the input lever or the crank-web 30 solid therewith engages the stop 34. Therefore, the control lever 20 moves very slightly in spite of the pressure exerted by the friction device 122. The eccentric 88 being adjustable permits of modifying the angle of rotation of crank-pin 43 of rotary valve member 40 and therefore of altering at will the magnitude of the movement of lever 20 to the right.

If the operator wishes to preset a constant eifort of predetermined value, he moves the control lever 20 to the right, for example from the centre of sector 118. Then crank-pin 60 rotates to the left, thus causing through rocker 87 and rod 92 the crank-pin 43 to pivot in the left-hand direction and to connect-the cylinder to the exhaust, so that the raising arms 18 are lowered. During this downward movement, rod 81 bends about its pivot pin 84. The weight of the instrument or equipment 2 causes the arms 18 to be lowered and to move the piston 37 in the 4hydraulic cylinder to the right (FIGURE 4), thus discharging the fluid therefrom. Thus, tool 2 is lowered and caused to penetrate into the soil. As a consequence of the resistance offered by the soil, the elort applied to the third-point strap 22 increases and the input lever 30 moves to the right and carries the crank-web 30 to the left. Crank-web 105 will rotate to the right and carry along link 89, eccentric pin S8, rocker 87, connecting-rod 92 and crank-pin 43 in the same direction. When this effort attains a value equal to the value preset bythe control lever 20 the rotary valve member 20 of distributor 12 will be in neutral position, for crank-pin 43 will have travelled in the opposite direction the same distance as imposed by the control lever 20, and the sinking movement of the tool 2 will be discontinued.

If the eort exerted on strap 22 became greater or lower than the preset effort, the servo-action linkage would become operative and cause the arms 1S to move up or down, according to cases. Thus, the tool 2 would be somewhat raised or sunk in the ground in order to restore after a short time period the desired effort which remains practically constant. Under these conditions, it is clear that in a same soil the tractive edort and the working depth corresponding thereto can be varied on purpose, provided that the soil is of homogeneous composition.

The operation of the device is particularly simple and easy to understand. The servo-action constantly regulates the vertical position of the tool or instrument so that the tractive elfort exerted by the tractor vehicle is constantly equal to a predetermined value preset by means of the control lever 20 on its sector 11S.

The operation of this device is extremely reliable due to the safety feature consisting of the accumulator spring 79, the limit rod S1 and the T-shaped slot formed in the deformable connecting-rods 66 and 92.

FIGURE 17 illustrates a modified embodiment of the device shown in FIGURE 14. In this alternate embodiment the two-section rods 66 and 92 of FIGURE 14 are replaced by one-piece rods 132 and 133, respectively. The transverse grooves or notches 74 and 190 of the aforesaid T-shaped slots are maintained at the free end of these rods, and the longitudinal slideways 73, 99 are replaced by their lower edge respectively, which constitutes in these rods the upper longitudinal side edge 134, 135 of their free end which is thus completely separable or detachable from the crank-pin 43 of rotary valve member 4t) (unidirectional coupling).

' In this modilied form of embodiment the angular amplitude of the movement of rotation of valve member 4t) in the raising direction (which is the counterclockwise direction as shown in the figure) by means of a fixed limit stop 136 rigid with the distributor body 36 and adapted to engage a counter-stop 137 solid with the rotary valve member 40.

The operation of this modified device is exactly similar to that of the preceding form of embodiment, but the construction is considerably simplified.

Of course, the present invention should not be construed as being limited by the specific forms of embodiment shown, described and suggested herein, as any modications may be brought thereto without departing from the scope of the invention as set forth in the appended claims.

What I claim is:

1. In a device comprising a power operating feedback servo-control system, responsive to manual and automatic sources of control modulation, for a tractor-borne implement three-point trailing hitch for upward and downward swing between raised transporting and lowered grounded working positions, the combination of a rockshaft journalled in a stationary support and operatively connected to said hitch for raising and lowering same and provided with drive arm means rigid with said rockshaft, a pressure-Huid actuated one-way ram unit including a cylinder dening a huid-expansible chamber with a reciprocating piston slidably mounted therein, a piston rod pivotally interconnecting said piston with said drive arm means, a source of pressure fluid supply connected through la transmission line to said chamber, a control valve mechanism inserted in said transmission line for selectively controlling delivery of said pressure fluid to said ram unit to raise said hitch and for exhausting said pressure fluid from said ram unit to lower said hitch, with a valve member shift-able in opposite directions and selectively settable in a fluid locking neutral medial posi- .tion effective to retain the actual position of said hitch and in either of two active end positions for raising and lowering said hitch on effect of respectively energizing and releasing said ram unit respectively, an adjustable draft load measuring and reflecting arrangement associated at a third attachment point of said hitch with sensitivity adjusting means and shiftable control means progressively movable in opposite directions in proportion to the draft load imposed on said hitch and with doubleacting balancing spring means resiliently opposing both forward and rearward tilting of said implement relative to said tractor to determine the extent vof displacement of said control means in either direction from a neutral position upon variation of said draft load, a positionresponsive valve-actuating first linkage responsive to the position vof said implement and positively interconnecting said rock-shaft directly with said valve member, a draft load-responsive valve-actuating second linkage posirocker.

Y tivelyfiriterconnecting lsaid controlY meansdirfectlyfWith- Y :niagaraV Y v said valve member, said linkages being separate and oper-j i able independently from each other,V extendingup to and` individually reaching said valve member and being 'ex-i clusively composed of hingedly interconnected rockersV and links providing la positively connecting andactuating y transmission, and each linkage` having an, operatorresponsive connection with said valve member, whereby in the engaged condltion of said connection the respec,

tive linkage is positivelyfandfvoperatively connected to said valve member whereas the-inoperative disengaged condition of saidconnection enables movement ofv saidv valve member independently of the linkage, a Vhand leverhaving an extended range of adjustmenhpivotedon said stationary support and for-med with lat least one crank wrist providing a selectively shiftable fulcrum, through which said hand lever is operatively connected to a command-initiating .link member of each linkage, Y said arm-means and tosaid crankV pin respectively and are fpr-I vided with means for-shortening of `saidjpull rod-upon.v Y reduction of vthe distance betweenits'v pivotsj and withY adjustablestop means to selectively limit jsaid Vdistance ink the extended condition of said pullr'od.V

7. A device according to'claim. 6, whereinfsaid pull 1 Y consists of two interlinked arms-with adjustable Ystop screw pivots of theA pull rod. Y *Y hand lever being adapted to be moved to and to be releas- Y ably secured in a selected position setting a predetermined magnitude either of saidV draft loadV or of saidvimplementl position, Vthe latter being then automatically maintained connected betweenfxedalugs andsaid force-transmitting by the corrective action of the corresponding linkage Vat a substantially constant value selectively variable throughV adjust-mentV of said hand lever and independent operator-r; responsive change-overmeanscontrolling said connection Vof Veach linkage to selectively conditionthe device alter-i- Y natively for controlling said first linkage or v,said second linkage,said change-over means being adapted tofdisable t either` one of said linkages andto simultaneously makethel` other operative 2. VA device according 'tto claim 1, further :comprising means carried by one gofsaidfarms and engageablek in'y abutting relationship by the other arm; uponstraightening, VV of said pull rod, the`V pivot `interlinking. said arms being offset with respect to the; center line joining; both of said Y 8. Acdevice accordingto claim 6,1wherein said force-V transmittinglinkslare each formed,{atsaidopposite ends,. Y with a substantially transverse/notch opening into ya 1on1 Y Vgitudinal side edge of therespectivecforcetransrnitting;link and towardsaid crank pinywhereby in said neutrali medial' position saidcrank'pin isr engageable in said:k notch upon.

upward swing ofthe respective force-transrnitting'linkandY .disengageable from, said 'notchuponVv ldownward swing thereof, :whereas individual Vdrawback springgmeans are.YV

links tourge the latter towardrespective engaged positions` Y 9'. A ,device according to ,claimr '8,3 further` 'comprising` stop meansfor limiting displacement ofsaidvalvemember,

10;A device according toclainir,V :wherein'said change-Y overmeanscornprise aturnbling shafttjournalled on'A a fixed support and o1'3e`r'atively;connectedv for rocking motion to a manual selectorl lever pivotedgtojsaid stationary Y support and :settableV in either` V:of two` extremempositions biasing spring means directly connected betweenfsaidk k Valve member and a iixed bracketv and adapted on the:

one hand to take up any slack'in the `actuallyoperative' one of Vsaid linkages, and on the other hand to urge said valve member toward its hitch-'raising position, and adjustable transport safety shut-off means directly ,intercom-i necting said rock-shaft with said valve member, positivelyf in ione directionA only, for automatically shifting said valve member to saidneutral medial position when said hitch( is raisedto a predetermined maximum height. i Y

3. A` device` according to claim 2, wherein said iirst. linkage comprises affirst rocker having one end pivoted tovoney of said crank wrists and yits other end pivotally connectedY to 'ione end of a first follow-up link the oppositel v end of which-is pivotally connected torsaid drivev armi means, said first rocker being pivotally connected intermediate `its ends to one endof a first force-transmitting i link the opposite end of which is pivotally` connectible: through one` of said connections with said valve member, `and whereinv said .'secondlinkage comprises Va second rockerhaving-onefend pivotedvto the othercrank wrist andits other end ,pivotally ,connected ,torrone end ofr aV second follow-up link the opposite end of which is operatively connected 4to said control means, said second rocker being pivotallyconnected intermediate its ends to one end wof la secondforce-transmitting link the opposite end ofz:

which'is pivotallyrconnectible through the ot-henconneot tion with said valve member.

.v 4. A device according to cl-aim f5,` wherein the pivotalY connection of said second rockerwith said second followv Y Vup link includes position adjusting means allowing variation of the, amount of relative displacement of said second 5.v A device according to claim/3, wherein saidfllink-' "ages and` said hand lever are movable in a substantially vertical plane ,and whereinsaid valve member is a sub-k stantially horizontal rotary plug formed end wise with .a crankweb provided with a crank pin to and `:fromwhich said force-transmitting links' are adapted to be alterna-l tively pivotally connected and disconnected, said biasing spring meansvbeing connected to said crank web. i 6. A device according to claim l5, wherein said shut-ofi means consist of a pull rod pivotedat its endsfto said drive i,

corresponding toV the, operative? conditions of saidviir'st linkage. or oftsaid second; linkage, respectively, said; turnbling4 shaft extending across s aid force-transmitting linksfinj i Y.

spaced relation thereto,1anda pair ofspaced disconnecting Y 1 lelements'integral with and radiallyrprojecting,from' said tumblingv shaftand registering each! with one force-transf` tion and vice versa. V y Y n, p K 11. A` device .according to claim liwhe'rcinfsaid dis-` connecting elements havecam-shapedjcontourslwith such i.

a profile as togcause both-forcetransmitting links to be simultaneouslytransiently disconnectedfrom saidrotary; Y plug in a determined intermediate position of saidrselector i lever. Y

12; iA devicev according V to claim 11,lfurther'comprising 1Y i Y "a vpair of lowergdraft links of adjustable length universally'y pivotedbetween the. rear end lof said tractor'a'nd; said im# Y plement, a top vlink of adjustable -rlengtligadaptedxto beV stressed for bothcompression and tension,7 pivoted at one end-to the upper end of an upright strutintegral withsaid implement andat thegotherendfto anuaperturedfrocker member pivotedtoV a x'edllug andrprovidedjwithrseveralw l holes increasinglyl spaced from .the pivot toffisaid rocker* Vmember toV allowv differingconnectio'ris witha pivotpin of said top link forvarying draft-load reilerctirng',rsensitivity', n

said balancing spring meansjacting upon Asaid'rocker-meirfifV ber to resisttilting thereof in; either direction and to retain Y itin a balanced condition, a pairn'of liftarmsriifi'gid withV Y said rock-shaft,a pair of drop links ofadjustabley length hingedly interconnecting said lift armsand said draftjlinks s intermediate the ends `of ysaid latter,y a bell-'crank' rockery lever journalled on said stationary support and havingonev Y arm pivotally connectedcthrou'gh anfadjustable,positiven-i fr transmission to said rocker memberand its otherarrn pivv i otallyl connected to saidoppositer end ofthe secondfollow-v up link, and two adjustable stop means limiting rocking of said bell-crank rocker lever in either direction and corresponding to maximum compression load and tension load respectively upon said top link to provide lock-out against the action of said second linkage.

13. A device according to claim 11, wherein said hand lever and said selector'lever are substantially coaxially mounted by means of a rotatably supported plain shaft integral with said hand lever and passing through a hollow shaft integral with said selector lever and rotatably mounted on said plain shaft, the device further comprising a slotted sector formed with at least one guide slot arcuate about the common pivot axis of said hand and said selector levers, and with at least two spaced gabs, said selector lever yieldably and slidably bearing sidewise against said sector and being adapted to engage said gabs in its two extreme positions, whereas said hand lever, which also rides on said sector, is fitted with resilient clamping means guidingly received in said slot and adapted to automatically retain said hand lever in any selected adjusted position in frictional contact with said sector, and relatively fixed position-adjustable stop means for said hand lever, at least one of which defines an uppermost lift position for said hitch.

14. A device according to claim 13, further comprising a housing at the rear end of said tractor, journalling said rock-shaft, enclosing and supporting said linkages of the device, said valve mechanism, said ram units and said piston rod, said housing form-ing an oil sump, a continuously driven pump having an inlet connected through a suction pipe to said oil sump and `an outlet connected through a discharge pipe to said valve mechanism, the latter comprising a casing formed with a pressure intake port connected to said discharge pipe, with an exhaust port opening into said oil sump, with a feed port connected through a duct to said ram unit, and with Aa main bore communicating, via corresponding ducts, with said ports and with said oil sump respectively, and accommodating said rotary plug, .a spring-loaded check valve inserted between said feed port and said main bore and formed with a member project-ing into said bore whereby said check valve is engageable by said rotary plug to be positively opened thereby, a spring-loaded exhaust valve inserted between said main bore and said exhaust port and consisting of .a plunger -sl-idably mounted in a chamber formed in said casing and communicating with said bore whereby said exhaust valve is adapted to be hydraulically closed, and an Ioverload relief valve fitted in said rotary plug and leading to said oil sump, said rotary plug being so shaped that when it is in neutral position, it blocks both delivery of said pressure fluid to, and exhaust of fluid from, said ram unit upon resiliently self-actuated closure of said check valve and spring-balanced opening of said exhaust valve, said rotary plug being rotatable in one d-irection fronrsaid neutral posit-ion to initiate the delivery of said pressure lluid to said ram unit upon feeding said chamber with pressure uid to hydraulically close said exhaust valve, said rotary plug being also rotatable in the opposite direct-ion from said neutral position to initiate the exhaust of said pressure fluid from said ram unit upon engaging said check valve to positively open it, on the one hand, and, on the other hand, allowing said exhaust valve-to open by allowing said pressure uid to be discharged from said chamber.

15. A device according to claim 11, wherein said forcetransmitting links are resilient only in a direction as to initiate disengagement of said crank pin from said transverse notch which opens into a longitudinal slot formed in the respective force-transmitting link, thereby allowing lost motion of said crank pin therein, said notch and said slot forming together a substantially T-shaped aperture.

16. A device according to claim 15, wherein said forcetransmitting links consist of two hingedly inter-connected parts fitted with a return spring permanently urging said parts toward a substantially aligned position in extension of each other, `one of said parts being formed with an abutment determining said aligned position and permitting bending of the respective link `only in a direction which initiates disengagement of said crank pin from said transverse notch, one of said parts of the link which is -pivoted to said rocker being engageable by the relevant one yof said cam-shaped disconnecting elements.

17. A device'according to claim 15, wherein said forcetransmitting links consist of two hingedly inter-connected parts fitted with a return spring permanently urging said parts toward a substantially aligned position in extension of each other, one of said parts -being formed with an abutment determining said aligned position and permitting bending of the respective link only in a direction which initiates disengagement of said crank pin from said transverse notch, one of said parts of the link which is pivoted to said rocker being engageable by the relevant one of said cam-shaped disconnecting elements.

18. A device according to claim 3, wherein said linkages and said hand lever are movable in a substantially vertical plane and wherein said valve lmember is a substantially horizontal rotary plug formed endwise with a crank web provided with a crank pin to and from which said force-transmitting links are adapted to be alternatively pivotally connected and disconnected, said biasing spring means being connected to said crank web.

19. A device according to claim 18, wherein said forcetransmitting links are each formed, at said opposite ends, with a .substantially transverse notch opening into a longitudinal side edge of the respective force-transmitting link and toward said crank pin, whereby in said neutral medi-al position said crank pin is engageable in said notch upon upward swing of the respective force-transmitting link and disengageable from said notch upon downward swing thereof, whereas individual drawback spring means are connected between fixed lugs and said force-transmitting links to urge the latter toward respective engaged positions with said crank pin.

20. A device according to claim 18, wherein said change-over means comprise a tumbling shaft journalled on a fixed support .and operatively connected for rocking motion to a manual selector lever pivoted to said stationary support and settable in either of two extreme positions corresponding to the operative conditions of said first linkage -or 'of said second linkage, respectively, `said tumbling shaft extending across said force-transmitting links in spaced relation thereto, and a pair of spaced disconnecting elements integral with and radially projecting from said tumbling shaft and registering cach with one force-transmitting link, said disconnecting elements being secured to said tumbling shaft in mutually angularly staggered relationship and adapted to alternatively engage and be disengaged from said force-transmitting links upon reciprocal rocking motion of said tumbling shaft in such a manner that when one force-transmitting link is operatively connected to said rotary plug in one of said extreme positions of the Aselector lever, the other force-transmitting link is disconnected therefrom in the other extreme position and vice versa.

21. A device according to claim 20, wherein said hand lever and said selector lever are substantially coaxially mounted on said plain shaft, the device further comprising integral with said hand lever and passing through a hollow shaft integral with said selector lever and rotatably .mounted on said plan shaft, the device further comprising a slotted sector formed with at least one guide slot arcuate about the common'pivot axis of said hand and said selector levers, and with at least two spaced gabs, `said selector` 19 r 520% If' i lever,- uatleast one of which denes an uppermost'lift po- 239961125 .153/61l 'Bunting r `;r sition for said hitch. v Y 

1. IN A DEVICE COMPRISING A POWER OPERATING FEEDBACK SERVO-CONTROL SYSTEM, RESPONSIVE TO MANUAL AND AUTOMATIC SOURCES OF CONTROL MODULATION, FOR A TRACTOR-BORNE IMPLEMENT THREE-POINT TRAILING HITCH FOR UPWARD AND DOWNWARD SWING BETWEEN RAISED TRANSPORTING AND LOWERED GROUNDED WORKING POSITIONS, THE COMBINATION OF A ROCK. SHAFT JOURNALLED IN A STATIONARY SUPPORT AND OPERATIVELY CONNECTED TO SAID HITCH FOR RAISING AND LOWERING SAME AND PROVIDED WITH DRIVE ARM MEANS RIGID WITH SAID ROCKSHAFT, A PRESSURE-FLUID ACTUATED ONE-WAY RAM UNIT INCLUDING A CYLINDER DEFINING A FLUID-EXPANSIBLE CHAMBER WITH A RECIPROCATING PISTON SLIDABLY MOUNTED THEREIN, A PISTON ROD PIVOTALLY INTERCONNECTING SAID PISTION WITH SAID DRIVE ARM MEANS, A SOURCE OF PRESSURE FLUID SUPPLY CONNECTED THROUGH A TRANSMISSION LINE TO SAID CHAMBER, A CONTROL VALVE MECHANISM INSERTED IN SAID TRANSMISSION LINE FOR SELECTIVELY CONTROLLING DELIVERY OF SAID PRESSURE FLUID TO SAID RAM TO RAISE SAID HITCH AND FOR EXHAUSTING SAID PRESSURE FLUID FROM SAID RAM UNIT TO LOWER SAID HITCH, WITH A VALVE MEMBER SHIFTABLE IN OPPOSITE DIRECTIONS AND SELECTIVELY SETTABLE IN A FLUID LOCKING NEUTRAL MEDIAL POSITION EFFECTIVE TO RETAIN THE ACTUAL POSITION OF SAID HITCH AND IN EITHER OF TWO ACTIVE END POSITIONS FOR RAISING AND LOWERING SAID HITCH ON EFFECT OF RESPECTIVELY ENERGIZING AND RELEASING SAID RAM UNIT RESPECTIVELY, AN ADJUSTABE DRAFT LOAD MEASURING AND REFLECTING ARRANGEMENT ASSOCIATED AT A THIRD ATTACHMENT POINT OF SAID HITCH WITH SENSITIVITY ADJUSTING MEANS AND SHIFTABLE CONTROL MEANS PROGRESSIVELY MOVABLE IN OPPOSITE DIRECTIONS IN PROPORTION TO THE DRAFT LOAD IMPOSED ON SAID HITCH AND WITH DOUBLEACTING BALANCING SPRING MEANS RESILIENTLY OPPOSING BOTH FORWARD AND REARWARD TILTING OF SAID IMPLEMENT RELATIVE TO SAID TRACTOR TO DETERMINE THER EXTENT OF DISPLACEMENT OF SAID CONTROL MEANS IN EITHER DIRECTION FROM A NEUTRAL POSITION UPON VARIATION OF SAID DRAFT LOAD, A POSITIONRESPONSIVE VALVE-ACTUATING FIRST LINKAGE RESPONSIVE TO THE POSITION OF SAID IMPLEMENT AND POSITIVELY INTERCONNECTING SAID ROCK-SHAFT DIRECTLY WITH SAID VALVE MEMBER, A DRAFT LOAD-RESPONSIVE VALVE-ACTUATING SECOND LINKAGE POSITIVELY INTERCONNECTING SAID CONTROL MEANS DIRECTLY WITH SAID VALVE MEMBER, SAID LINKAGES BEING SEPARATE AND OPERABLE INDEPENDENTLY FROM EACH OTHER, EXTENDING UP TO AND INDIVIDUALLY REACHING SAID VALVE MEMBER AND BEING EXCLUSIVELY COMPOSED OF HINGEDLY INTERCONNECTED ROCKERS AND LINKS PROVIDING A POSITIVELY CONNECTING AND ACTUATING TRANSMISSION, AND EACH LINKAGE HAVING AN OPERATORRESPONSIVE CONNECTION WITH SAID VALVE MEMBER, WHEREBY IN THE ENGAGED CONDITION OF SAID CONNECTION THE RESPECTIVE LINKAGE IS POSITIVELY AND OPERATIVELY DISENGAGED SAID VALVE MEMBER WHEREAS THE INOPERATIVE DISENGAGED CONDITION OF SAID CONNECTION ENABLES MOVEMENT OF SAID VALVE MEMBER INDEPENDENTLY OF THE LINKAGE, A HAND LEVER HAVING AN EXTENDED RANGE OF ADJUSTMENT, PIVOTED ON SAID STATIONARY SUPPORT AND FORMED WITH AT LEAST ONE CRANK WRIST PROVIDING A SELECTIVELY SHIFTABLE FULCRUM THROUGH WHICH SAID HAND LEVER IS OPERATIVELY CONNECTED TO A COMMAND-INITIATING LINK MEMBER OF EACH LINKAGE, SAID HAND LEVER BEING ADAPTED TO BE MOVED TO AND TO BE RELEASABLY SECURED IN A SELECTED POSITION SETTING A PREDETERMINED MAGNITUDE EITHER OF SAID DRAFT LOAD OR OF SAID IMPLEMENT POSITION, THE LATTER BEING THEN AUTOMATICALLY MAINTAINED BY THE CORRECTIVE ACTION OF THE CORRESPONDING LINKAGE AT A SUBSTANTIALLY CONSTANT VALUE SELECTIVELY VARIABLE THROUGH ADJUSTMENT OF SAID HAND LEVER AND INDEPENDENT OPERATORRESPONSIVE CHANGE-OVER MEANS CONTROLLING SAID CONNECTION OF EACH LINKAGE TO SELECTIVELY CONDITION THE DEVICE ALTERNATIVELY FOR CONTROLLING SAID FIRST LINKAGE OR SAID SECOND LINKAGE, SAID CHANGE-OVER MEANS BEING ADAPTED TO DISABLE EITHER ONE OF SAID LINKAGE AND TO SIMULTANEOUSLY MAKE THE OTHER OPERATIVE. 